In conventional elevator apparatus speed governors, a first overspeed Vos (an activating velocity of an operation stopping switch) is set to approximately 1.3 times a rated velocity Vo, and a second overspeed Vtr (a safety activating velocity) is set to approximately 1.4 times the rated velocity Vo. If it is detected that the car has exceeded the rated velocity and reached the first overspeed Vos due to an abnormality in the controlling apparatus, for example, power supply to a hoisting machine is interrupted to stop the car urgently. If the car is falling due to breakage of a main rope, etc., the second overspeed Vtr is detected by the speed governor, and a safety device is activated to make the car perform an emergency stop.
However, if the car is positioned in a vicinity of a terminal floor of a hoistway, the car may reach a bottom portion of the hoistway before the car velocity increases to the first overspeed Vos and the second overspeed Vtr, and in that case the car is decelerated and stopped by a buffer. For this purpose, the buffer requires a longer buffering stroke as the velocity that must be decelerated increases, and the length of the buffer is determined by the first overspeed Vos and the second overspeed Vtr.
In answer to that, a method has also been proposed in which a car position switch is disposed in a vicinity of the terminal floor to detect an abnormality and shut off the power supply to the hoisting machine at a terminal overspeed Vts that is lower than the first overspeed Vos when the car position switch is operated.
Thus, provided that the main rope is still connected to the car, the car velocity will not exceed the terminal overspeed Vts. If, on the other hand, the main rope breaks when the car is positioned in a vicinity of a lower terminal floor of the hoistway, it is not possible to brake the car using the hoisting machine even if the terminal overspeed Vts is detected.
In that case, if Ts is the time from when the main rope breaks until the car collides with the buffer, then the impact velocity Vs is:Vs=Vts+g×Ts If this impact velocity Vs is lower than the second overspeed Vtr of the speed governor, then it is possible to shorten the buffering stroke of the buffer proportionately.
However, in recent years, there is demand for additional space saving and cost saving, and there has been demand for buffer dimensions to be shortened further, and speed governors have been proposed in which the first overspeed Vos and the second overspeed Vtr are reduced in the vicinity of terminal floors (see Patent Literature 1 and 2, for example).